AS FILED WITH THE SECURITIES AND EXCHANGE
COMMISSION ON MARCH 21, 2013

FILE NO. 333-160918

FILE NO. 811-22321

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER THE SECURITIES ACT OF 1933 x

Post-Effective Amendment No. 41
x

AND

REGISTRATION STATEMENT

UNDER THE INVESTMENT COMPANY ACT OF 1940 x

Amendment No. 43

MAINSTAY FUNDS TRUST

(exact name of registrant as specified in
charter)

51 MADISON AVENUE, NEW YORK, NEW YORK 10010

(address of principal executive office)

REGISTRANT'S TELEPHONE NUMBER: (212) 576-7000

J. Kevin Gao, Esq.

MainStay Funds Trust

169 Lackawanna Avenue

Parsippany, NJ 07054

Copy to:

Sander M. Bieber, Esq.

Dechert LLP

1775 I Street, NW

Washington, DC 20006

(NAME AND ADDRESS OF AGENT FOR SERVICE)

It is proposed that this filing will become effective

x

Immediately upon filing pursuant to paragraph (b) of Rule 485

o

on ________ pursuant to paragraph (b)(1) of Rule 485

o

60 days after filing pursuant to paragraph (a)(1) of Rule 485

o

on ________, pursuant to paragraph (a)(1) of Rule 485

o

75 days after filing pursuant to paragraph (a)(2) of Rule 485

o

on ________ pursuant to paragraph (a)(2) of Rule 485

If appropriate, check the following box:

o

This Post-Effective Amendment designates a new effective date for a previously filed post-effective amendment

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and
the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this
Registration Statement under Rule 485(b) under the Securities Act and that it has duly caused this Post-Effective Amendment No.
41 to its Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Parsippany
in the State of New Jersey, on the 21stday of March, 2013.

MAINSTAY FUNDS TRUST

By: /s/ Stephen P. Fisher

Stephen P. Fisher

President and Principal Executive Officer

Pursuant to the requirements of the
Securities Act of 1933, this Post-Effective Amendment No. 41 to the Registration Statement has
been signed below by the following persons in the capacities indicated on March 21, 2013.